Microplate technology has thrived thanks to the desire to avoid radioactive assays and the need to measure more samples faster, at lower volumes, and in parallel. Analysis software, nonradioactive assays, and robotics (e.g., plate handling, automated liquid handling) are the technologies that enable microplate readers to do their magic. Without appropriate software, data generated by highdensity plate readers would overwhelm scientific staff, as would handling and pipetting thirty 384-well plates.
“Users are used to software being intuitive—something they can pick up and run with,” observes Kasia Proctor, global product manager at Molecular Devices (Sunnyvale, CA). The company’s SoftMax Pro monitoring and control software has been available in iPad format since 2011. The iPad platform permits users to upgrade the software’s capabilities by adding instrument or analysis-specific “apps” instead of installing a patch or upgrade.
Small volumes are desirable because they allow higher sample density per plate and save on reagents and sample. However, plates beyond 96 or 384 wells are employed mainly for highthroughput screening. For routine work one quickly reaches a point of diminishing returns. “There are, in some ways, unrealistic expectations for smaller and smaller samples,” Proctor says.
Many microplate experiments are still conducted manually, but even low-volume operations are beginning to appreciate the consistency and quality of results associated with mechanical and data automation.
The value of ongoing nonradioactive assay development cannot be overestimated. “The application of luciferase for luminescence, of europium and terbium for timeresolved fluorescence, and of fluorescent proteins for fluorescent intensity or polarization have all greatly expanded the functionality of microplate readers,” says E. J. Dell, Ph.D., international marketing director at BMG Labtech (Ortenberg, Germany). These detection modes have made possible real-time phosphorylation assays using fluorescent polarization rather than radioactive ATP, or celldeath assays through time-resolved fluorescence rather than radiolabeled chromium. “With more and more applications developed specifically for the microplate format, the everyday use of microplate readers will only increase.”
Microplate readers are a stable, mature market. “For us, the main trends involve machines with the same basic detection capabilities, but greater flexibility and ease of use,” says Xavier Amouretti, product marketing manager at BioTek Instruments (Princeton, NJ). The industry is in the same stage, he adds, as the cuvettespectrometer market, which has not changed in terms of assay capabilities for many years but has become higher-performing and more user-friendly.
Most readers today are built for upgradability. One of the most popular “flex” strategies is to purchase a relatively inexpensive unit with monochrometer optics only. Once the system is up and running, a service technician can add filter-based detection in about two hours. “This will add several detection modes to your system,” Amouretti observes.
Molecular Devices’ SpectraMax Paradigm reader platform allows users to swap out fluorescence detection cartridges themselves, without a visit from the technician. The cartridges contain 90 percent of the required optics, says Proctor.
According to Dell, during the past five years microplate readers have undergone “major advances that have broadened their use” and have “transitioned from being a luxury item in a well-financed facility to being a mandatory piece of equipment for a new start-up laboratory.” BMG Labtech has introduced technologic advances related to absorbance detection and bottom reading (required for cell-based assays).
Until quite recently, microplate absorbance measurements could be performed only with filters or monochromators, limiting researchers to a single number per measurement. Multiple-wavelength assays required multiple reads. Now that a CCD-based spectrometer can be incorporated into the reader, users can conduct full-spectrum reads in under one second per well.
The second innovation solved the problem of low sensitivity during bottom-reading. For this, BMG introduced its Direct Optic Bottom Reading, which precisely focuses light on the plate bottom where cells are located, thus improving the signal-to-noise ratio. Dell claims a 300 percent improvement in S:N with the new system.
Darren Cook, VP for strategy and business development at Douglas Scientific (Alexandria, MN), suggests that purchasers of microplate readers should consider the following factors:
• Usage: Will the system be served in a dedicated, production- like environment, or will it run periodically?
• Longevity: Future needs should be considered, but not overly so, as chemistry and detection modes continue to evolve and improve.
• Detection mode flexibility: Do present and anticipated future needs demand flexibility in experimental design, or is the reader being purchased for a specific project or task requiring a single or very few detection modalities?
• Throughput and parallelism: Will the unit serve a high-throughput application running 24/7 (a process that is time-sensitive, requiring only short but high-intensity runs), or is the application relatively flexible in terms of scheduling? Consider a highly parallel instrument or perhaps the purchase of two, less feature-rich instruments.
• Sensitivity and capacity: These factors depend highly on the experiments and assays, and should be considered early on in the evaluation process.
• Upgradeability: Upgradable systems may be purchased at a lower price, and modified later as needed.
• Service and support: Aside from preventing downtime and problem solving, top-notch service and support can assist users in getting the most from their readers.
Cook explains, “Ultimately, my best advice is to ensure you get the right tool for the job. I can recall many instances from my personal life where not having the proper tool cost me many multiples of what a project should have cost had the right tool been available.”
BioTek’s Amouretti suggests purchasers consider support, software, and applications, with software paramount. “You deal with it every time you use the instrument, and 90 percent of what you’re doing concerns software, so make sure it is intuitive and doesn’t require you to spend half your time trying to get it to do what you want.”
BMG’s Dell observes that purchase decisions always involve the proper balance of features and price. Features to consider include sensitivity, speed, number of detection modes, plate format compatibility, and “extras” such as spectrometer, reagent injectors, shaking, incubation, gas vent, bottom reading, etc. “If price is a constraint and you cannot afford all of the features you like,” Dell adds, “consider a system capable of upgradability.”